Hello Jurgen,
Thanks for the reply. these were the thoughts too, so deleted the delivery and sales order and re created the sales order and DO, but the same behavior is repeated and no clue to this erratic happening
no doubtful methods 
like table entry etc were done. all through standard sap and material creation mode
any suggestions...some more info, Material is non valuated and does not have value updation in material type but has batch management active, but in development the indicator is set for these too
Thanks
Akash